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doi:10.2204/iodp.proc.318.107.2011

Operations

Transit to Site U1359

We began transit to Site U1359 at 1530 h on 7 February 2010. While departing the shelf, we had to negotiate around and through an assortment of pack ice and grounded ice bergs; these became less concentrated and finally disappeared as we moved off the shelf. As we arrived in the vicinity of Site U1359 at midnight, we experienced near–gale force winds, rough seas, and visibility down to 4 nmi in freezing rain. We lowered the thrusters and stabilized near the site using the Global Positioning System but waited on the weather to improve until the next morning (Table T1). The 73 nmi transit to Site U1359 was accomplished in 8.5 h at 8.6 kt. All times in this section are given in local ship time, which was Universal Time Coordinated + 11 h.

Site U1359

Hole U1359A

After 7 h, the weather conditions improved enough so that we could assemble the drill string to the seafloor. We started APC coring in Hole U1359A at 1800 h on 8 February 2010 with the bit at 3012 meters below rig floor (mbrf). Based on recovery of the first core, the water depth was 3020.9 mbrf, 9.1 m deeper than the corrected depth from the precision depth recorder. Cores 318-U1359A-1H through 17H penetrated to 145.4 mbsf and recovered 124.27 m (86%). Temperature measurements were made while taking Cores 318-U1359A-4H, 7H, 10H, and 13H (29.1, 57.6, 86.1, and 114.6 mbsf, respectively). Nonmagnetic core barrels were used for all piston cores after Core 318-U1359A-1H but were not oriented. After APC refusal, we deepened the hole with XCB Cores 318-U1359A-18X through 22X from 145.4 to 193.5 mbsf and recovered 29.81 m (62%). Total recovery for Hole U1359A was 80%. Rather than continuing to deepen the hole with the XCB, we decided to stop so that we could core two more APC holes to provide a more complete section.

The bit cleared the seafloor at 1700 h on 9 February, and we offset the vessel 25 m west-southwest.

Hole U1359B

Coring in Hole U1359B began at 1815 h with the bit at 3017 mbrf. Seafloor was established at 3018.8 mbrf. APC Cores 318-U1359B-1H through 23H penetrated to 209.0 mbsf and recovered 183.59 m (88%) (Table T1). Nonmagnetic core barrels were used for all APC cores. We deepened the hole with XCB for Cores 318-U1359B-24X through 28X from 209.0 to 252.0 mbsf and recovered 15.33 m (36%). The total recovery for Hole U1359B was 79%. The bit was pulled clear of the seafloor at 2240 h on 10 February, and the vessel was offset 25 m west-southwest of Hole U1359B.

Hole U1359C

Coring in Hole U1359C began at 2340 h on 11 February with the bit at 3020 mbrf. Seafloor depth was established at 3022.3 mbrf. APC Cores 318-U1359C-1H through 18H penetrated to 168.7 m and recovered 150.73 m (89%). We planned to stop coring at this time to be able to depart for high-priority shelf sites so that we could take advantage of a forecasted period of good weather. We planned on returning to this site, so we did not retrieve the seafloor beacon at this time. The bit cleared the seafloor at 1620 h and was back onboard at 2340 h on 11 February. We departed for Site U1360 at 2345 h on 11 February. The total time on Site U1359 was 89.25 h.

Return to Site U1359

After operations at Site U1360 and multiple attempts to return to that site and other shelf sites, we returned to Site U1359 at 2200 h on 19 February 2010.

Hole U1359D

A RCB bottom-hole assembly was assembled and lowered to the seafloor. Seafloor was tagged with the bit at 3023.0 mbrf, and drilling started at 0530 h on 20 February. We drilled without coring to 152.2 mbsf and then started RCB coring at that depth to overlap with previous APC/XCB coring that had penetrated to 252 mbsf. RCB Cores 318-U1359D-2R through 48R penetrated from 152.2 to 602.2 mbsf and recovered 269.7 m (60%). The last core was recovered on deck at 1145 h on 23 February.

In preparation for downhole logging, we flushed the hole with a 50 bbl mud sweep and made a wiper trip up to 82.6 mbsf and then back down to 602.2 mbsf. After another 50 bbl sepiolite mud sweep, we released the bit at the bottom of the hole, displaced the hole with 191 bbl of 10.5 ppg mud, and raised the end of the pipe to 96.9 mbsf for logging.

We were able to conduct two very successful logging runs in excellent hole conditions. The triple combo and FMS-sonic tool strings were able to log the entire hole from 602 mbsf up to the end of the pipe. The FMS-sonic tool string was back on deck at 2000 h on 23 February. In accordance with our Marine Mammal Protocol, we waited until daylight the next day before conducting the check shot log utilizing the Schlumberger VSI.

We rigged up the VSI and started lowering it downhole at 0745 h on 24 February. The VSI was able to reach within 5 m of bottom of the hole, but we had to postpone starting the check shots because a few whales had entered within the mammal exclusion zone. Once we were able to start, we discovered that the VSI caliper arm could not be extended to clamp the tool against the borehole wall. However, we were able to set the tool on the bottom of the hole and get good enough coupling with the formation to collect data at that depth. We could have retrieved the VSI tool for repair/replacement, but we decided conclude logging so we could attempt to reach one of our high-priority shelf sites. After we recovered the VSI at 1330 h on 24 February, we retrieved the drill string, with the end of the pipe clearing the seafloor at 1440 h and arriving back on the rig floor at 2050 h. We departed for the last attempt at occupation of one of the high-priority shelf sites at 2245 h on 24 February.

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